Fluoropolymer hollow fiber membrane with fluoro-copolymer and fluoro-terpolymer bonded end portion(s)

ABSTRACT

A hollow fiber membrane fluid transport device is disclosed wherein the fibers are comprised of Polytetrafluoroethylene (PTFE), and the potting materials are comprised of fluorocopolymer and or fluoroterpolymer based materials. The potting of the device utilizes a compressed chemically resistant fluorocopolymer and or fluoroterpolymer film, allows for ease of manufacture without destruction of the PTFE hollow fibers, with high packing densities, and without the processing complexity of pre-melting, extruding, or chemical crosslinking of any polymeric adhesives. Furthermore, the PTFE hollow fibers can be treated with a fluoropolymeric solvent solution before the chemically resistant film is applied to enhance the adhesion of the PTFE fiber to the film. PTFE hollow fibers, and its respective fluoro-co and terpolymers as potting films impart high packing densities, superb chemical resistance and temperature resistance without membrane contamination, or low fiber pull strength, as is sometimes observed with standard potting materials such as polyurethane and epoxy.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Division of application Ser. No. 13/065,183, filedMar. 16, 2011 now U.S. Pat. No. 8,540,081. This application is not aDivision of International Patent Application No. PCT/US12/29439.

FEDERALLY SPONSORED RESEARCH

Not Applicable

SEQUENCE LISTING OR PROGRAM

Not Applicable

BACKGROUND (FIELD)

This application relates to hollow fiber membrane fluid transportdevices, specifically to the method of manufacturing such membrane fluidtransport devices, and even more specifically to the means of assemblingthe hollow fibers into bundles and sealing the ends of the hollow fibersto make suitable contactors.

BACKGROUND OF THE INVENTION

Membrane contactors are useful devices for separation processes,contacting processes, or as filters. A membrane contactor includes amembrane or membranes held in such a manner as to separate two regionsof flow and enable the membrane to act as a separation means between thetwo phases, and a housing to enclose the membrane and contain and directthe flow of the multiple phases. The membrane acts as a barrier betweenthe two fluid phases and selectively allows or prohibits the transportof one or more chemical species or particles from one fluid stream tothe other. The housing has one or more ports to allow flow to and fromthe membrane. Membrane contactors can be considered as a subclass of themore general class of fluid or fluid/gas transport devices.

Membrane contactors have applications as filters, separation systems, orcontacting devices in many industries such as chemical, pharmaceutical,food and beverage, environmental, water treatment, and semiconductorprocessing. Membrane separation processes such as gas/liquid separationor membrane distillation are replacing their bulk counterparts(distillation towers, stripping columns) due to improved energyefficiency, scalability, the ability to operate isothermally, andsmaller physical footprints. In addition, membrane filters, separators,and contactors generally have no moving parts and are physically simpleand rugged, resulting in low maintenance cost.

Hollow fiber membrane devices are one class of membrane modules thatemploy membranes in hollow fiber form. While many types of membranes areavailable in sheet form, the ability to create significantly highersurface area per unit volume with a hollow fiber membrane is of majoradvantage to the designer and user of a membrane filter or contactor. Ahollow fiber membrane is also typically self-supporting in contrast toflat sheet or thin film membranes that usually require a skeletalstructure for support. In addition, typical contactor designs employinghollow fiber membranes, whether constructed as a cross flow element orin a dead-end configuration, offer more uniform flow and fewer regionsfor the flow to stagnate.

The usefulness and efficiency of a membrane contactor is determined bythe available surface area of the membrane per unit volume of the deviceand the rate at which the transfer or removal of the species of interestoccurs; this is generally governed by the flux (flow per unit area, perunit time, per unit pressure gradient) of the process stream. Theavailable surface area for a hollow fiber membrane module is dictated bythe packing density of the fibers (the ratio of the sum of the crosssections of the individual fibers to the total available cross sectionalarea). The higher the packing density and the greater the surface areato volume ratio generally results in a more efficient module.

Two other useful parameters for defining the performance of a porousmembrane are the pore size distribution and the porosity. The pore sizedistribution is a statistical distribution of the range of porediameters found in the membrane wall. The largest pore size is alsogenerally characterized by a measurement called a bubble point, which isdefined in the below detailed description of the invention. The smallerthe mean pore size, the smaller the particle a membrane filter willseparate.

The porosity of a hollow fiber membrane may be defined as the percentageof free volume in the membrane, or, for PTFE hollow fiber membranes, as(1−(membrane density/2.15)*100 where 2.15 is the density of solid PTFE.The higher the porosity, the more free volume and generally the higherthe flux rate through the membrane wall.

For a given pore size distribution, higher porosities are oftendesirable as they lead to higher flux rates. Unfortunately higherporosities also generally lead to softer membrane walls, causing thehollow fibers to be structurally very soft and prone to deformation andcollapse, especially during a potting process. Heating the ends of thehollow fibers reduces the porosity and hardens the heated portion of thefibers, reducing the likelihood of the fibers being crushed or deformedon compression.

The elements of a hollow fiber membrane contactor include the hollowfiber membrane itself, the housing, and a means to bind the fibers toone another and to the housing. A hollow fiber membrane is a porous ornon-porous, semi-permeable membrane of defined inner diameter, definedouter diameter, length and pore size, and generally of a very highaspect ratio, defined as the ratio of the length to the diameter of thefiber. A hollow fiber membrane contactor is generally comprised of aplurality of fibers.

The housing is an outer shell surrounding the membrane that secures andcontains a potted bundle of hollow fibers. The housing is equipped withone or more inlets and one or more outlets, such that the potted bundleof hollow fiber membrane acts as a barrier and separates the two phasesor process streams. The design of the housing, and specifically therelationship of the inlets and outlets, regulates the flow of theprocess fluid into or out of the fiber lumens and directs the processedfluid away from the device. There are typically two common modes ofdesigning the housing, which relate to how the fluids interact with themembrane. What are known to those well versed in the art as dead-endelements consist of a housing that directs all of the volume of onefluid to pass through the membrane walls to reach the discharge or exitof the housing. The dead-end design is a very common design employed formembrane filtration. For dead-end hollow fiber membrane filters, bothends of each hollow fiber membrane are potted or bound at one end of thehousing. In dead-end hollow fiber membrane filters the process fluideither enters the lumens of the hollow fibers and discharges out throughthe walls of the hollow fiber membrane, or enters through the walls anddischarges out of the lumens. In either case, this ensures that theentire process stream passes through the membrane wall.

A dead-end hollow fiber membrane filter configuration is contrasted to across flow configuration in which the lumens are open at both ends, andonly a portion of the process stream entering the upstream lumens passesthrough the membrane wall, while the remainder of the fluid dischargesthrough the downstream lumen openings. The portion of the fluiddischarging from the downstream lumen end may be passed along to anothermembrane element, recycled to the beginning of the unit, or discarded.The cross flow configuration mode is employed with both filtration aswell as membrane contacting or separation processes.

A hollow fiber membrane bundle may be integral to the housing or may bedesigned so that the potted hollow fiber membrane bundle may beinstalled and removed.

To create a membrane filter or membrane separator or contactor module,one must establish a suitable means for binding the hollow fibermembranes into an integral bundle and sealing the exposed ends of thehollow fibers from the body of the module, a process hereafter referredto as potting the fibers. Potting the hollow fiber membranes may occurprior to, or during the operation of mounting the hollow fiber membranesinto the housing. To bind the ends of the hollow fibers to one another,a potting compound is employed. A potting compound is a material thatwhen applied around the ends of hollow fibers, bonds them together intoa solid, cohesive mass that isolates and fixes the hollow fibers fromthe remainder of the bundled assembly of fibers.

A potted bundle of hollow fibers is a plurality of hollow fibermembranes bound together or potted at least at one end. Both ends may bepotted, or the ends of each individual fiber may be looped back in aU-shape and potted at or near one end. One potential configuration canbe where the bundled fibers are first twisted 180 degrees and thenfolded into itself to form a closed end and an open end with the openend potted, i.e.—embedded in a solid mass providing a fluid-tight sealaround each fiber. There may be several themes and variations on thesebasic configurations.

Membranes for contactors or filters have been developed from a varietyof synthetic polymers and ceramics and have been known in the industryfor many years. While ceramic membranes offer the chemical resistanceand high service temperature required by aggressive acidic, alkali, ororganic solvent applications, in their present-day state they are veryfragile, very expensive, and very difficult to work with, a combinationof features that keeps ceramic membranes out of many applications.

The vast majority of state of the art polymeric membranes are limited asthey are not inert, they possess inadequate chemical purity, thermalstability and chemical resistance, and occasionally have undesirablesurface properties, preventing their use in certain importantapplications. This is because these very same membranes are spun fromsolution, and the fact that they must be soluble in certain solvents toconvert to a membrane means that the final membrane itself issusceptible to attack by those same classes of solvents.

It has long been desired to be able to have membranes manufactured fromfluorinated or perfluorinated resins due to their high servicetemperatures, chemical stability, inertness, and chemical resistance toa wide range of solvents, acids and alkali systems. However, membranesproduced from non-fully fluorinated polymers still require aggressivesolvent systems and very high processing temperatures to manufacture,increasing cost and generating environmental and waste issues. Membranesmanufactured from Polytetrafluoroethylene (hereafter referred to asPTFE) are most desirable because, as a fully fluorinated polymer, theyoffer the best combination of thermal and chemical stability of all thefluorinated and perfluorinated resins commercially available. Inaddition, the method by which they are converted to membranes does notemploy hazardous solvent systems; instead using a stretching andorientation method.

It is also desirable to have membranes manufactured from fluorinated orperfluorinated resins, especially fully fluorinated resins, due to theirlow surface energy Filtration of organic liquids, separating organicfrom aqueous systems, or removing vapor from aqueous systems all favorlow energy membranes. PTFE offers the lowest surface energy of all thefluorinated or perfluorinated polymeric membranes—less than about 20dyne-cm.

Current potting materials have many limitations such as inadequatechemical resistance, lack of chemical purity and inertness, and poorthermal stability. They are also very difficult to use, and produceinefficient and costly modules. One such class of inadequate pottingsystems consists of low viscosity materials including urethanes andepoxies which are easy to apply but are chemically very impure and arenot chemically resistant, nor do they offer high service temperatures.

It is also therefore highly desirable to have a potting compound thathas excellent chemical resistance and high service temperatures thatwould match those of the fluorinated, perfluorinated, or fullyfluorinated membrane, because the effectiveness of a contactorconstructed with a fluorinated or perfluorinated membrane for athermally or chemically aggressive system is limited by the weakest partof the device. An effective combination of a potting system for afluorinated or perfluorinated membrane has hitherto been unavailable.Current potting methods are not amenable to the use of fluorinated orperfluorinated compounds; they cannot produce membrane modules with highfiber packing density, or with economical manufacturing cycle times; norcan they be employed to make contactors with relatively soft fibers orcontactors containing many thousands of fibers, something necessary formany commercial membrane applications.

PRIOR ART

In the art, various adhesives, such as epoxies, polyurethanes,cyanoacrylates, etc. have been used for bonding or potting the ends ofhollow fibers together into an integral assembly (for example, H. Mahon,U.S. Pat. No. 3,228,876, Mahendran et al. U.S. Pat. No. 6,685,832).These systems offer the advantage that the potting compound flowsreadily between the fibers, but methods utilizing these adhesives forpotting fluoropolymer membranes in general and PTFE membranes inparticular suffer from serious limitations. The adhesion of epoxies,cyanoacrylates, and polyurethanes to fluoropolymer fibers, in general,and PTFE in particular, is very limited, resulting in assemblies thatsuffer from fiber pullout and failure due to pressure or thermalcycling. More importantly, materials such as epoxies, polyurethanes,cyanoacrylates, etc. suffer from very limited chemical and thermalstability, thus greatly limiting the types of high temperatures or harshor aggressive chemical environments for which one would want to use PTFEhollow fibers.

Some practitioners avoid the use of potting compounds such as epoxies,polyurethanes, cyanoacrylates, etc. via melt bonding the fibers,eliminating the use of potting compounds all together. Melt bonding hasit's own limitations.

Muto et al. (U.S. Pat. No. 5,066,397), Suzuki et al. (U.S. Pat. No.7,291,204B) and other practitioners teach methods for assemblingthermoplastic hollow fiber membranes via a fusion process. In both theSuzuki and the Muto fusion process at least one set of the ends of thehollow fibers are bundled together and heated above the softening pointof the hollow fibers allowing the ends to form into a solid end terminalblock. PTFE however will not fuse with itself unless exposed totemperatures in excess of 340° C. and very high pressures (greater than50 bar). Exposure to the extreme temperatures and pressures would crushthe fibers and destroy the porous structure, thus rendering the Mutoprocess and others like it, that require a melting or softening of thehollow fiber membrane, unsuitable for PTFE. The fusion method employedby Muto, Suzuki, and others also suffers from the limitation of notbeing able to control the fiber spacing, something necessary for highsolids filtration applications or larger high flow rate contactors wherethe tightness may restrict the flow.

Spiegelman et al. (U.S. Pat. No. 7,625,015) teaches the use of aconnector with a series of pre-drilled holes through which fibers areplaced and then crimped in place via an external swaging ring. A majorlimitation of the Spiegelman method is that the fibers must have asignificant degree of rigidity to maintain the seal. Sealing with atight clamp as required by Spiegelman would crush the soft PTFE fibersand a tight, leak proof seal would not be achieved. This method wouldnot be suitable for contactors with desired high packing density.

U.S. Pat. No. 5,695,702 (Niermeyer) teaches a technique for building andsealing the ends of hollow fiber membranes into a module by contactingan array of hollow fibers with an extruded molten thermoplastic polymer.The molten thermoplastic polymer flows over and in between the hollowfiber ends as they are assembled into an array. The process as describedby Niermeyer is not effective for PTFE hollow fibers and not asefficient as the present invention herein for any fluoropolymer fiberfor several important reasons. The Niermeyer process requires that themolten thermoplastic polymer be heated and applied at a contacttemperature higher than the melting point of the hollow fiber membrane.This allows the material to flow between the fibers and more importantlyresults in at least partial melting of the hollow fiber membrane wall toform an integral bundle. For PTFE hollow fiber membranes, heating thefiber or exposing the fiber to temperatures near or at its melting point(327° C.-345° C. depending on degree of sinter) would destroy theintegrity of the fiber, changing the pore structure of the hollow fiber.

In addition, as known by those practiced in the art, the type ofthermoplastic polymers cited in Niermeyer that are capable of beingextruded into an unsupported molten web, are very viscous in theirmolten state; and thus, it would require large gaps between the fibersto allow the melt to flow between the fibers; a critical requirement toform a leak free potted assembly. The Niermeyer technique requires thatthe molten polymer flow quickly between the fibers before the next layeris applied on top or the unit will leak. This flow is driven strictly bygravity, as there is no means of forcing the melt between the fiber. Thespacing between the adjacent fibers and between layers of fibers islarge, resulting in poor fiber packing density and loss of efficiency ofthe finished unit.

Huang et al. (U.S. Pat. No. 5,284,584) teaches a method very similar toNiermeyer, as Huang also utilizes a melt extrusion potting method.However, in Huang, the molten thermoplastic extrudate used for pottingmust have a melting point 10° C. or lower than that of the fiber, whilein Niermeyer the extrudate is at a higher temperature than that of thefiber. Although this overcomes the limitation of having to use extremetemperatures for extrusion potting utilized in the Niermeyer patent,Huang does not address the issue that the use of a melt for pottingprohibits high packing density of the fibers. However, this impartsanother limitation, as cited by Niermeyer, the lower temperature usedfor potting in Huang limits the use temperature of the finished devicemade by such a technique. Most limiting is that Huang also claims thatthe fiber tubes are only thermoplastic. Huang also only claimspolyolefinic tubes, and more highly prefers (in the specification)polyolefin tubes as well as polyolefinic potting agents.

Cheng et al. (U.S. Pat. No. 6,663,745 and its patent family) teaches amethod employing a perfluorinated polymer for potting perfluorinatedhollow fibers which overcomes only some of the difficulties outlinedearlier. In Cheng, a solid mass of a perfluorinated polymer is heatedand degassed in an oven to a molten state and a set of looped hollowfibers are suspended in a hole created in the molten polymer. Driven bygravity, the molten potting polymer flows between the hollow fibers,filling the voids between the fibers. The resultant mass is cooled,annealed, and the bottom of the potted mass is cut off to reveal theopen lumens. The Cheng method contains severe method and practicallimitations for commercial hollow fiber modules. Cheng teaches thatpreparation of the potting polymer requires that the polymer be held atelevated temperatures 16 to 72 hours, and preferably 24 to 48 hours, toallow melting and degassing in the oven. The Cheng process requires theuse of a polymer with a low enough melt viscosity to flow freely throughthe fibers, greatly limiting choices of potting materials, an additional16 to 24 hours for the polymer to diffuse in amongst the hollow fibers,and an additional 16 to 24 hour annealing step following potting for acombined assembly time from 48 hours to five days.

The Cheng patent is also limited to smaller bundle diameters as the timerequired to diffuse into the center of larger units would be excessive,resulting in burnt polymer, very high assembly costs and the risk ofvoids in the potted assembly. Because Chung requires the unaided flow(other than gravity) of a highly viscous fluid between the fibers, thefiber packing density cannot be high, severely limiting the use of thecontactor due to surface area limitations. Cheng also cites exampleswhere the addition of a wire grid for spacing is required to achieve apacking density of only 60% for this reason. Addition of grids and otherfiber spacing techniques adds cost and time to construction, as eachfiber must be individually threaded through the mesh. The use of suchgrids would be unimaginable for typical commercial modules that employthousands of fibers.

In WO2000/044483A2 (Yen, filed Jan. 27, 2000), Yen claims a methodsimilar to Niermeyer, but for potting an all perfluorinatedthermoplastic fiber membrane device. The Yen method also claims that aTFE/HFP or TFE/Alkoxy tape can be used in a potting method. However, Yenspecifically prohibits the use of PTFE hollow fibers in his patentapplication, even excluding the use of PTFE in the claims: Yen statesthat PTFE is not a thermoplastic and that it is difficult to mold andform into various shapes. Of equal commercial concern is that thepacking density in the Yen device is very low (as is the packing densityof other potted systems in the literature carried out via a meltextrusion process) compared to the packing density of the inventionherein. All of the polymer melt flowing potting methods are limited bythe need to maintain significant spacing between the fibers toaccommodate the flow of the very viscous polymer. Yen specifies 45-65%packing density in the preferred mode with the stated reason as to avoidincomplete potting and the formation of voids. Like the Niermeyerpotting method, the Yen method has no control of packing thickness andpacking density, and requires considerable time to assemble even a smallunit. The Yen method also calls for a required post-potting heattreatment to ensure no voids or leaks in the potted end, a step thatadds considerable additional costs for assembly.

In comparison to Niermeyer and Huang, the polymeric film potting methodstated herein has the advantage of eliminating the need to allow spaceand time for a molten polymer to flow between the fibers. The filmpotting method also offers additional advantages over the Niermeyerprocess when applied to PTFE hollow fibers, in that the fibers may bespaced significantly closer to one another as no unessential space isneeded for the flow of a very viscous fluid. In addition, polymeric filmas a potting agent doesn't typically flow into the open holes at the endof the hollow fibers, so one doesn't have to add the additional methodstep of cutting and removing open fibers filled with potting agent.

The invention herein also overcomes limitations of Cheng. The filmpotting method is suitable over a wide variety of bundle diameters,including the number of fibers and choice of potting polymers.Furthermore, the present invention allows the designer to generatetightly packed fiber bundles or to deliberately create spacing betweenthe fibers to enhance flow on the shell side of the module. In addition,larger units with greater numbers of fibers and the ability to controlpacking density offer significant design advantages to the end user. Thefilm potting method stated herein also has advantages over the methodsin the Muto and Spiegelman patents as it is a more gentle process and itdoes not lead to the crushing of the fibers. The film method also doesnot result in fiber contamination, as does methods using epoxies,polyurethanes, cyanoacrylates, and other non-fluoropolymers as pottingagents.

As is apparent from the limitations cited in the above art, forfluorinated, and perfluorinated hollow fiber membranes in general, andPTFE hollow fiber membranes in particular, there exist many needs forimprovements in potting methods that have not yet been satisfied. Thelimitations in the art and current day commercial potting needs arereemphasized below.

The ideal potted end has a long lasting and robust bond between thepotting medium and the hollow fiber (the fiber must have strong adhesionto the potting compound so that the fibers cannot be pulled or pushedout under the temperature and pressure cycles of normal operation).Preferably, the potting method minimizes or eliminates any distortion ordeformation that would otherwise damage or hurt the integrity of thehollow fiber. If the fiber is collapsed or distorted, a flow restrictionmay result, and the ensuing module would be less efficient. If the fiberis collapsed or damaged, the fiber may leak under subsequent operation,resulting in a defective module. A distorted fiber may not fully bondwith the potting material, resulting in a flow path between the fiberwall and the potting compound, or between the fiber and shell, orpotting material and shell, resulting in a leak and a defective module.

The ideal potting material is of a nature that it's thermal resistance,chemical resistance, chemical inertness, and chemical composition, donot limit the use of the hollow fibers, that is, the chemical resistanceand service temperature of the potting material ideally would match orcome close to matching that of the membrane itself. The potting compoundgenerally is as chemically robust as the hollow fiber membrane or therange of applications of the module will be diminished and the end userwill not be able to capitalize on the desired properties of themembrane.

The ideal potting method allows for efficient packing of fibers, meaningthat the fibers can be packed closely together, accommodating as manyfibers in the cross sectional area of the module as possible. The idealpotting method allows for control over the packing density of the fiberso that the designer can accommodate high solids level applications,high flow applications, and other conditions that may dictate largerspacing between fibers. The ideal potting method accommodates or isadaptable to any number of fibers as filters and contactors may rangefrom a few fibers up to many thousands. The ideal potting methodaccommodates a wide range of fiber diameters without having to sacrificemodule construction efficiency or packing density. The ideal pottingmethod accommodates a wide range of fiber porosities and of varyingsoftness. Finally, the marketplace dictates that the potting methodshould be cost effective, low in labor and short cycle times.

As will be disclosed, the invention that is the subject of this patentovercomes inadequacies of prior art as well as meeting desiredcharacteristics outlined above.

DESCRIPTION OF THE DRAWINGS

The operation of the present invention should become apparent from thefollowing description when considered in conjunction with theaccompanying figures, in which:

FIG. 1: Illustration of a typical array of hollow fibers

FIG. 2: Support frame with hollow fibers wound over ends

FIG. 2a Examples of frame end elements with varying spacing

FIG. 2b Examples of frame end elements with varying spacing

FIG. 3: Support frame with hollow fiber being wound over ends

FIG. 4: End view of hollow fibers with first weave tape

FIG. 5: Isometric view of hollow fibers and first weave tape

FIG. 6: Isometric view of hollow fibers with two weave tapes

FIG. 7: End view of hollow fibers with first weave tape and upper crosstape

FIG. 8: End view of hollow fibers with first weave tape and one crosstape

FIG. 9: Isometric view of hollow fiber web with completed tapes

FIG. 10: End view of spiral wrapped hollow fiber web

FIG. 11: End view of spiral wrapped hollow fiber web with colletcompression

FIG. 12: End view of spiral wrapped hollow fiber web with adjustablesleeving

FIG. 13: End view of compressed and fused hollow fiber bundle

FIG. 14: View of cross flow potted hollow fiber bundle

FIG. 15: View of web prepared for dead end filter element

FIG. 16: Completed dead end filter element

SUMMARY OF THE INVENTION

The posited challenges of potting or sealing soft hollow PTFE fibermembranes are addressed by the system of the present set forth below.The system reliably and rapidly seals PTFE hollow fibers together andfills the interstices between the fibers. Materials are identified thatare chemically and physically compatible with both the hollow fibermembrane and the process fluids to be used in the contactor module.Additionally, the present system provides a device that incorporates thesaid potting system. The polymeric film potting system presented hereinovercomes the challenges listed above by: not requiring the fiber wallto be softened (by excessive heating), by ensuring the bondingthermoplastic resin (in the form of a polymeric film) is in between eachadjacent fiber, and by allowing very close fiber spacing, and highpacking densities (due to the compressing means). This is alsoaccomplished without the longer processing time necessary for a viscousmaterial to flow under gravity in between the fibers.

The potting method described herein offers advantages over pottingmethods disclosed in the art for fluoropolymer membranes in general andPTFE membranes in particular. These advantages include: the ability toeconomically produce potted fiber bundles with high packing densitiesregardless of the diameter of the fiber or of the unit, applicabilityregardless of how soft the hollow fiber membrane, the ability toeconomically produce a wide variety of diameters and length modules, andshort cycle times, regardless of the nature of the fiber or size of theunit.

The potting polymeric film utilized in the present system can be definedas any type of generally flat material whose length and width aresignificantly greater than its thickness, and usually, although not arequirement, whose length is far greater than its width. The pottingfilm can have a thickness that is less than the diameter of the hollowfibers down to less than one hundredth of the diameter of the hollowfibers. It is ideal that the film be as thin as possible. In fact, thefilm can be very thread like in thickness, as long as it can be handledduring manufacture. The length of the potting film (along the length ofthe hollow fiber) can be less than, or equal to, the diameter of thebundled fibers down to less than one hundredth of the diameter of thebundled array of fibers. Thinner film results in a higher fiber packingdensity. The width of the film can be equal to the length of the film,although the width is variable, as the more fibers that are used, themore film is needed to surround each fiber. It is preferred that thefilm be applied as close to the ends of the hollow fibers as possible,so that upon melting it does not flow into the hollow fibers. It is mostpreferred that the length of the portion of the film along the length ofthe hollow fiber is even with the ends of the hollow fiber, so that uponmelting, the melted film does not flow into the ends of the hollowfibers. Any type of chemically resistant thin film can be used to form aweb over the ends of fiber bundled in a generally parallelconfiguration. Herein, the film may be very chemically resistant and canbe chosen from the list of perfluorinated copolymers of: TFE/HFP,TFE/Alkoxy, TFE/PPVE, TFE/CTFE, and copolymers of Ethylene such asEthylene/TFE, Ethylene/FEP, and other similar fluorinated polymers suchas DuPont™ SF-50 and Solvay™ Hyflon 940 AX, or fluorinated terpolymersof Ethylene/VDF/HFP (Dyneon™ THV).

In another embodiment the fluoropolymer or other polymer used for thefilm or potting compound may be dissolved in a solvent such as acetone,butyl acetate, ethyl acetate, N-methyl pyrrolidone, or methyl ethylketone to create an adhesion promoter or primer solution. One preferredpolymer solution is comprised of fluorinated terpolymers ofEthylene/VDF/HFP (Dyneon™ THV) and butyl acetate. The dilute adhesionpromoter solution may be applied to the ends or near the ends, or forthat matter on any portion of the porous PTFE hollow fibers where thefilm will be applied, allowing the adhesion promotion solution to wickor infuse into the pore structure of the hollow fiber. Upon drying orremoval of solvent, the residual polymer or adhesion promoter that isinfused into the inner pores of the fiber promotes enhanced adhesionbetween the potting film and hollow fibers.

According to one aspect, the present invention provides a fluidtransport device having a plurality of perfluorinated polymer fibersthat have an inner diameter and an outer diameter. At least one end ofeach fiber is open for fluid entrance or exit. The fibers aresubstantially parallel to one another and a length of polymeric filmbonds the fibers together by contacting outer surface areas of thefibers adjacent ends of the fibers and filling interstitial volumebetween the fibers

According to another aspect, the present invention provides a hollowfiber membrane fluid transport device comprising a cylindricalcontainment shell containing polytetrafluoroethylene hollow fiberstreated with a solvent polymer solution. The solution comprises apolymer used to prepare a potting film so that after solvent removal bydrying, the fibers are bound together in bundles by at least one segmentof film interwoven through interstitial spaces between the fibers andcontacting each fiber near or at the ends of the bundles of the fibers.

According to yet another aspect, the present invention provides a methodfor producing a hollow fiber membrane fluid transport device. The methodincludes the step of laying polytetrafluoroethylene hollow fibers in anarray or a row. Fluorinated homopolymer, copolymer, or terpolymer filmis applied to the hollow polytetrafluoroethylene fibers interwovenbetween the fibers near one end or both ends of the hollowpolytetrafluoroethylene fibers. The fibers and film are rolled into abundle. A portion of the bundle is then heated and compressed to meltthe film such that the film melts and flows between the hollow fiber toform an integral bundle of hollow fibers. The bundle is the cooled toform a solid mass providing a fluid-tight seal around each fiber suchthat the ends of the hollow fibers are open on one side of the solidmass and the open fiber ends are isolated from the fiber walls of themembrane.

According to a further aspect, the present invention provides a methodfor producing a hollow fiber membrane fluid transport device. Accordingto the method, a plurality of polytetrafluoroethylene hollow fibers arearranged in an array or a row. A fluorinated homopolymer, copolymer, orterpolymer film on the hollow polytetrafluoroethylene is applied to thefibers so that the film is interwoven with the fibers near one end orboth ends of the hollow polytetrafluoroethylene fibers The fibers andfilm are rolled into a bundle. The bundle is heated and compressed tomelt the film such that the film is applied to the fibers at a contacttemperature lower than the melting point of the fibers thereby causingthe hollow fibers to form a bundle of hollow fibers. The bundle is thencooled to form a fluid-tight seal around the fibers such that the endsof the hollow fibers are open on one side of the solid mass and the openfiber ends are isolated from the fiber walls of the membrane.

DETAILED DESCRIPTION OF THE INVENTION

This invention provides a simple, fast, and reliable method forproducing a membrane contactor comprising a plurality of hollow fibermembranes produced from polytetrafluoroethylene or other fluoropolymersemploying a potting compound comprising of a perfluorinated orfluorinated thermoplastic to seal the ends of the hollow fibers and bindthem into a solid mass. The invention further provides for the membranecontactor or filter module made by the inventive method.

The hollow fiber membranes used in this invention are produced frompolytetrafluoroethylene homo or copolymers, but the technique isapplicable to any polymeric or inorganic hollow fiber membrane, andrepresents an excellent technique for potting ceramic hollow fibermembranes as it minimizes risk of breakage of the fragile fibers.

The potting film that is used in this invention may be produced from anyfluorinated or perfluorinated thermoplastic such as: PFA(polytetrafluoroethylene perfluoropropyl vinyl ether), FEP(perfluoroethylene propylene polymer), MFA (polytetrafluoroethyleneperfluoro methyl vinyl ether), PVDF (polyvinylidene fluoride), THV(tetrafluoroethylene, hexafluoropropylene, vinylidene fluorideterpolymer), EFEP (ethylene perfluoroethylene propylene polymer), ECTFE(ethylene chlorotrifluoroethylene polymer), ETFE (ethylenetetrafluoroethylene polymer), or other fluorinated or perfluorinatedthermoplastics. Preferred compounds are EFEP and THV for lowertemperature applications (below 120° C.), MFA and PVDF for applicationsup to 150° C., and FEP or PFA for applications up to 200° C.

The potting film may be any of a variety of commercially availablefluoropolymer or perfluropolymeric films manufactured from the resinslisted above (DeWal Industries, Ajedium, are examples of commercialsuppliers) or may be extruded as a film via a melt extrusion andcalendaring operation known to those practiced in the art or produced bycompression molding granules, powder, or pellets into a thin filmbetween two heated platens, or cast from a solution prepared fromgranules, powder, or pellets of the resins listed above. The preferredmethod is a film produced via extrusion and calendaring operation.

The film is prepared to a thickness of between 0.01 mm and 2.5 mm, withthe preferred thickness between 0.076 mm and 0.125 mm and is generallydependent on the spacing desired between the fibers and the diameter ofthe fibers.

Shown in FIG. 1, the construction of a two dimensional plane of fibers10 is the starting point for the film potting method and this twodimensional plane of fibers is hereafter referred to as the web 5. Theweb can be prepared via different techniques. A number of hollow fibersof a given diameter and porosity are placed in a substantially parallelarrangement by either securing individual fibers to a support frame, orby wrapping a single length of hollow fiber multiple times around asupport frame or by any other such means as to generate a twodimensional plane of fibers held stationary and parallel to one another.

The support frame may be one of any number of suitable types of designs,but generally consists of three or four sides lying in the same plane,approximating a rectangle where each of the opposite pairs of sides aresubstantially parallel to one another. As shown in FIG. 2, the pair ofsides opposite to one another that serve as either the terminal pointsfor the fibers or the ends over which the fiber is wrapped around arereferred to collectively as the frame end elements 12. The other side orpair of sides opposite to one another that are substantially parallel tothe hollow fibers are referred to as the side elements of the frame 14.It is preferred that the side element 14 or elements 14 are adjustable,allowing the frame end elements to be move apart from one another,enabling the frame to be used for multiple module lengths. It is alsopreferred that the end frame elements 12 are removable to allow eitherthe spacing between the fibers to be adjustable or to adjust the widthof the web being prepared. FIGS. 2a and 2b show two such types of endframe elements.

While individual fibers may be arranged along the perimeter of a frameand secured, one embodiment as shown in FIG. 3 is to wind a singlehollow fiber 10 around the end frame elements 12, creating two webs 5 offibers, an upper web and a lower web, or one long web of double thelength of the frame. The frame may be stationary and the fiber wrappedaround the frame, or the frame may be rotated about an axis runningparallel to the end frame elements 12 as the fiber is fed to the frame.The hollow fibers may be wound around a cylindrical mandrel, however,the use of the cylindrical mandrel is not as preferred as it inhibitsthe later weaving process and requires a different cylinder for eachlength of module desired.

It is also preferred that the spacing between fibers is maintained at adistance approximately equal to or slightly greater than the thicknessof the potting film being employed, allowing the assembler the abilityto control the spacing between the fibers and hence control the spacingbetween fibers in the final module. The spacing may be controlled byutilizing a few different methods. One method to control the spacing isto use frame end elements, examples of which are shown in FIGS. 2a and2b that have a series of parallel grooves 15 or slots perpendicular tothe major axis of the frame end element. A second method is to use aseries of circular disks of known thickness placed in between adjacentfibers. In lieu of circular discs a variety of fin or comb-likestructures that allow the fibers to be indexed at uniform spacing alongthe length of the frame end element can also be used. It is generallydesirable that the spacing be equal at the two opposite frame endelements to ensure equal spacing between the fibers in the completedpotted assembly.

A primer may be applied to further improve bonding between the pottingfilm and the porous fiber. A dilute solution of the potting resin usedto manufacture the potting film is prepared by dissolving either thefilm, pellets, granules, or powder forms of said potting resin in asuitable solvent. For a film produced from THV 220 may be suitablydissolved in acetone or methyl ethyl ketone. The percent solids in thesolvent will be a function of the molecular weight of the polymer, butthe solution should be suitably dilute to allow the film deposited topenetrate the pore structure of the fiber. A solution of 6 to 10% solidsby weight is suitable, but solutions more dilute, down to 1% solids byweight are also acceptable and as high as 15% solids by weight willwork. As the solids level increases, the penetration into the porestructure decreases and the thickness of the dried primer on the outsideof the fiber increases.

If used, the primer solution is brushed or wiped onto the fiber endswhere the potting film is to be applied, preferably covering the entirecircumference of the fiber membrane. Additionally, preferably the primersolution is limited to covering only the portion which will eventuallybe covered by the potting film, because the primer penetrates the porestructure of the membrane and can block pores. The primer is allowed todry in air for a minimum of two hours at 20° C. to 30° C. Whileapplication of heat will accelerate the drying process, this is lesspreferable as there is risk of forming bubbles from the solvent beingreleased too quickly. After the primer has dried, the fiber array isready for application of the film for the next step in the pottingprocess.

Whether or not a primer is employed, the next step in the film pottingprocess is to begin applying strips of potting film to the ends of thefiber web. As shown in FIG. 4, typically a length of thin film 20,preferably a fluoropolymer, is inserted between the fibers 10 in adirection substantially perpendicular to the major axis of the fibers ator near either of the frame end elements. FIG. 5 shows an isometric viewof the fibers with one strip of film woven between them. The film 20 isfirst fed over the top of the first fiber 10 and underneath the adjacentfiber 10. This sequence repeating itself in such a way as to ensure thateach fiber has at least one layer of the film between that fiber andeach adjacent fiber until all the fibers have been separated from oneanother by one layer of film.

The thin film 20 may be a single strip woven between the fibers, or, asshown in FIG. 6, may consist of two or more strips 20 of film wovenbetween the fibers in alternating directions next to one another, withthe first strip passing over alternate fibers, the adjacent strippassing under those same alternate fibers, resulting in a longer pottedportion of fiber. A second strip of film or set of film strips may thenbe woven in a similar manner at the opposite frame end element,depending on the type of module to be constructed. If the element is tobe a cross flow element or a dead end filter element, both ends arefitted with the strips of film. If the web is to be unfolded to a doublelength, then no strips are applied at the opposite frame end element.

Following the insertion of one or more lengths of thin film alternatingbetween the fibers, a length of thin film 22 is then placedperpendicularly to the major axis of the fiber as shown in FIG. 7, ontop of the array of fibers and along the same axis as the strips of filmpreviously woven between the fibers. This strip of film may be wider ornarrower than the band of woven strips, but preferably is of the samewidth as the combined width of the woven strips and is referred to as acrossing film. The thickness of this first crossing film may be ofvariable thickness, chosen by the assembler to control the distancebetween the fibers as they are bundled. Use of a crossing film is notnecessary, but can help to ensure that the potted end is leak-free andalso helps to control spacing between the fibers.

The crossing film and the woven film are then heated at a temperaturethat is greater than 10° C. above the melting point of the polymer fromwhich the film was made until the crossing film fuses with the wovenfilm strip or strips.

After bonding crossing strips to the woven strips at either or both endsof the frame, the frame may be flipped over and the process repeated onthe reverse side at top and bottom, creating two identical webs readyfor the last step prior to bundling. For a single web of double length,only one end on the reverse side is potted.

After applying the weave strips and the crossing strips, the web isremoved from the frame. If the web was prepared by wrapping a hollowfiber, the fibers are cut along the major axis of the frame end elementsseparating the fibers into two webs, one formed on the top of thewinding rack, one on the bottom. If only one end of the top web andbottom web were prepared with the fluoropolymer films, then the web isopened up on itself to form a single web of a length double that of thewinding frame.

The single web or the two matching webs are then placed on a flatsurface, with the face having the upper crossing film face down. Asecond crossing strip 24 is then placed along the woven strips, as shownin FIG. 8, parallel to the previously applied crossing strip, but on theopposite sides of the fibers. If the opposite ends of the fibers werefitted with film, then a second crossing tape is applied to that end aswell. FIG. 9 shows the completed web 5 of fibers 10 with woven film 20and upper 22 and lower 24 crossing strips applied at both ends of theweb.

On completion of the individual web, it is carefully rolled up uponitself as shown as an end view in FIG. 10, allowing the ends of thefibers fitted with the strips of film to wind up in a spiral 30.Additional webs may then be wound onto the roll simply by abutting theend of one web with the beginning of the other, having trimmed anyexcess of the film from the ends of each. Additional webs are applieduntil the final fiber count is achieved. The web may be wound up onitself or may be wrapped around a core piece to provide support orstructure. The core piece may be a fluoropolymer rod or may be machinedfrom stainless steel or other compatible metals or polymers. If one usesa metal core, it is important that the surface be roughened orpre-coated with a fluoropolymer that is compatible with the film usedfor potting to ensure good adhesion and no leakage between the fibersand the solid core piece.

The potted fiber bundle is completed by a combination of applied heatand compression. Radial compression of the taped end by heating andcompressing means causes the fiber ends to translate radially toward thecenterline of the cylindrical bundle, reducing the distance betweenadjacent fibers until all interstitial volume between the fibers iseliminated and the fused tape contacts all outer surfaces of themembranes. This results in a leak proof potted end. The compression andapplied heat are essential for establishing void-free, leak free highpacking density potted ends.

The radial compression may be achieved by any number of means takinginto account several factor. It is desirable to compress the bundle at arate that limits or avoids deforming the hollow fibers and/or causes thefibers to become closed off. It is also desirable to compress the bundlein a manner that maintains a substantially rectangular cylindrical shapeto the potted end. The end fitted with the strips of film is heated to atemperature at least 10° C. above the melting point of the film andallowed to reach equilibrium. The time required to reach equilibrium isdictated by the size of the module.

The compressing means may be by several methods, all of which achieve agradual compression and maintain a cylindrical shape while being heated:including but not limited to: heat shrinkable sleeving, various colletsystems, adjustable centerline roller systems, and an adjustablesleeving system. There are other methods of achieving the compressionthat would be obvious to those skilled in the art on understanding thefunction of the compression.

Achieving compression via a collet system as shown in FIG. 11 consistsof placing the rolled end 30 of the fibers fitted with the woven andcrossing films in a collet system 31 of a diameter large enough toaccommodate the rolled and uncompressed bundle whose closed diameter isequal to or less than the desired final compressed diameter of the fiberbundle. The collet assembly holding the bundle of fiber fitted with thepotting films is placed in an oven or heated chamber and brought up to atemperature at least 10° C. above the melting point of the film used forpotting.

Achieving the compression via an adjustable sleeving system as shown inFIG. 12 is achieved by placing a suitable band 35 of tempered steelaround the rolled bundle 30. The band consists of a strip of metal thathas preferably been coated with PTFE or similar release agent. The widthof the band should be no wider than the length of the potted region ofthe fibers. The band should overlap on itself by at least 5% andpreferably about 25% to maintain a uniform circle and so when radiallycompressed via a circular clamp 23, the end of the band slides over topof itself and reduces in diameter in proportion to the tightening of theouter band clamp. The thickness of the tempered steel is between 0.1 mmto 0.127 mm, but may be as thin as 0.0254 mm for smaller bundles and asthick as 0.05 mm for larger diameter bundles.

The fiber bundle is compressed until the desired final diameter isachieved and all the voids between the fibers have been eliminated. Thefinal diameter may be simply where all the voids are eliminated but maybe reduced more by further tightening of the bundle. The compressedpotted end is removed from the heat source and allowed to cool at whichtime the compression means is removed from the potted end.

Depending on the number of fibers, the diameter of the fibers, thesoftness of the fibers, and the final diameter desired in the bundle,the compression means may be achieved in a single step or multipleapplications. For larger bundles, generally exceeding 50 to 80 mm indiameter, benefit from multiple applications of the compression meansduring build-up of the fibers. FIG. 13 shows an end view of the pottedfibers 10 in the solid mass of potting compound 35.

For a cross flow module, the final bundled assembly has two potted ends40, each of which resembles the potted cross section shown in FIG. 13.FIG. 14 shows a drawing of such a potted bundle.

To achieve a similar configuration for a dead-end or single potted end,one prepared end of the web 5 is flipped over on itself (FIG. 15) whileholding the other end stationary, resulting in the web 5 being twistedalong the plane of the web with the result that the top strip 22 at oneend of the web no longer lies in the same plane as the top strip 22 onthe other end of the web. The web is then rolled and compressed in amanner similar to that previously outlined resulting in a potted bundlewith looped fibers 10 shown in FIG. 16.

Fiber Potting Characterization

To validate the integrity of the potted end, a test may be provided toshow there is no leakage around the fibers between the fiber wall andthe potting compound at elevated pressures. In the present instance, amethod common to those practiced in the art was employed which involvesthe determination of the bubble point of the fiber using isopropylalcohol. The bubble point method includes a number of steps. In thefirst step the fiber is wetted in isopropyl alcohol (IPA) andpressurized to ensure there is no trapped air in the pores of the fiber.The fiber is then looped and immersed in a clear container of IPA withthe two lumen ends above the level of the IPA. Air pressure is appliedto the lumen ends in small increments until the first bubble of air isobserved on the outside of the fibers. The resulting pressure is thebubble point pressure and is an indication of the largest pore in thefiber as the IPA in that pore is the most readily (lowest pressure)displaced by the incoming air pressure.

The integrity of a potted end may be tested by sealing the potted end ina clear tube of plastic or glass and immersing the pendant hollow fibersin IPA. Air pressure is applied to the open lumen ends of the hollowfibers and the potted end is observed as well as observing the firstappearance of a bubble on the fiber walls. If no bubbles appear at thewetted face of the potted end and the bubble point pressure matches thatof the single fiber, the integrity of the potted seal has been shown.

To test the strength of the bond between the fiber and the pottedassembly, a pull test has been developed that measures the forcerequired to extract a single fiber from the potted end of the bundle (orbreak the fiber attempting extraction). The test consists of using aChatillon Force Gauge on an individual fiber from one of the potted endsof the bundle. The bundle is placed under the slotted support bracket tohold it in place. An individual fiber is randomly selected, placedthrough the slotted support bracket, and tied to a “J” hook attached tothe top of the force gauge. The force gauge is activated and extendsupward pulling on the individual fiber to achieve separation from thepotted bundle or breaking of the individual fiber, whichever comesfirst. Once the end point is reached, the machine automatically stopsand displays the break force value in Newtons.

COMPARATIVE EXAMPLE 1

Twenty hollow fibers with an outer diameter of 1.5 mm and an innerdiameter of 1.0 mm and a porosity of 55% were potted using an epoxypotting compound formulated by Henkel Corporation (Loctite®) for usewith fluoropolymer resins.

Two samples were prepared, with the fibers for the first sample leftuntreated while the fibers for the second sample were treated with aCorona Discharge to promote adhesion with the epoxy. The coronadischarge consisted of five second exposures four times followed byrotation of the fiber by 90° and repeating the treatment until the fiberhad been rotated 360°.

The epoxy was Loctite product X263572, developed expressly for use withfluoropolymers and other low surface energy polymers. Approximately 350grams of resin were mixed with 122 grams of hardener. A fixture was madeto suspend the fibers in a 100 ml beaker so that they did not touch thesides or the bottom of the beaker. The fibers were looped over the topof a rod so that the ends of the fibers were suspended in the resin.

The epoxy was cured for 10 hours at 22° C. followed by 2 hours at 65° C.and 2 hours at 120° C. to achieve a complete cure. Following cooling toroom temperature for 4 hours, the beakers were removed and the bottom2-cm was cut off from each potted end. The ends were polished to achievea clean finish on the potted ends.

The adhesion between the fiber and the potting resin was tested using aChatillon force gauge attached to an individual fiber and pulled tofailure. In each case the failure mode was the fiber pulling free of theepoxy. For the untreated fiber, the average pull force required to pullout the fiber was 3.37 lbf or 15 Newtons. The treated fibers had anaverage pullout force of 7.53 lbf or 33.5 Newtons.

EXAMPLE 1

In this example, the film potting method is used to make a cross flowmodule of 110 hollow fibers potted at both ends of the bundle.

110 loops of a hollow fiber membrane prepared frompolytetrafluoroethylene with an inner diameter of 1.5 mm and an outerdiameter of 1.9 mm with a porosity of 40% were wrapped around a windingframe 400 mm from end to end and 250 mm wide. The winding frame wasfitted with slotted rods at each end, with spacing between slots of 2.0mm, ensuring spacing between the hollow fibers of 0.1 mm.

A potting film pre pared from Ethylene Fluorinated Ethylene Propylenecopolymer (EFEP, Daikin RP 4020) with a thickness of 0.0762 mm, a widthof 25.4 mm, and a length of 220 millimeters was woven between eachindividual fiber at the end of the winding frame. The film was passedunderneath the first fiber on the frame and then alternately passed overthe top of the next fiber and underneath the following fiber. Thispattern was repeated until the film was passed between each fiber on thewinding rack. The excess tape was trimmed off. A second strip of tape ofsimilar size was placed on top of the hollow fibers (referred to as thetop tape), directly above the woven strip. The end of the winding rackcontaining the tape was heated above its melting point of 160° C. bymeans of a forced air heat gun set at 450° C. for 45 seconds. Thepotting tapes melted sufficiently to attach to each other and to thehollow fibers.

The weaving process was repeated at the other end of the winding rack,followed by application of a top layer of film heated and bonded to thefibers and the woven film. The process was again repeated on the twoends on the back side of the winding rack.

The fibers were removed from the winding rack by cutting the fibersalong the major axis of the slotted ends containing the tape, formingtwo webs of fibers bound by the potting tape. Each woven web containing110 fibers was laid on a flat surface with the side fitted with the toptape facing downward. A third piece of potting film of similardimensions (bottom film) was placed over the hollow fibers directlyabove the other two films and heated in a similar manner, bonding thetwo strips of film to one another and to the hollow fiber.

The first web was subsequently wound into a tight cylinder, beingcareful that the ends remained parallel and that the diameters of eachend were identical. The second web was subsequently added to the end ofthe first web and continued to be wrapped, resulting in a final diameterof approximately 38 mm in diameter.

To compress the bundle ends and occlude any voids, each taped end wasfitted with a sleeve of a fluoropolymer heat shrink with an innerdiameter of 38 mm (FEP 160 DuPont, 1.3:1 expansion ratio) approximately25 mm long. Each taped end was then placed in an oven at 232° C. for 30minutes. The heat shrink tubing reduced in diameter, compressing thebundle of fibers into a contiguous mass. The resulting mass was allowedto cool for 30 minutes. The fluoropolymer heat shrink was then cut fromthe potted end.

The potted bundle final diameter was 32 mm with a packing density of78%. Examination of the potted ends via optical microscopy revealed novoids in the potted ends and good contact between the EFEP potting resinand the fibers. The resulting module was pressure tested by using themethod outlined above and found to be fluid tight.

Subsequent testing of the individual fibers showed a pull strength ofgreater 75 Newtons, with the fiber failing before the bond with thepotting.

EXAMPLE 2

In this example, the film potting method is used to produce a dead-endfilter module. A continuous length of porous PTFE hollow fiber with thedimensions of 1.0 mm inner diameter and 1.5 mm outer diameter, with aspecific gravity of 0.9 grams/cm³ was employed for this module. Usingthe winding apparatus previously described in Example 1, the fiber waswound between the two end pieces 120 times to create two 120-fiber webson the top and bottom of the winding frame. The spacing between thefibers was maintained by machined grooves in the end pieces of thewinding frame. The spacing between the fibers was set at 1.6 mm. Thespacing between the two end elements of the frame was 610 mm. Thisprocess was repeated several times to generate sufficient fibers to makethe unit.

A strip of 0.051 mm thick THV-220G film (Dyneon) with a width of 50 mmwas woven in between the porous hollow fibers following previouslydescribed methodology at the two ends of the winding frame. Afterweaving one strip of film at each end of the winding frame, anotherstrip of film of identical dimensions was placed directly over the topof the fibers. Using an industrial heat gun set at 450° C., hot air waspassed over the film for approximately 30 seconds. The film was fused tothe individual fibers as well as to the underlying film. This processwas repeated on the opposite end of the frame. The frame was rotated toexpose the opposing side and a second strip was applied over the wovenstrips at both ends of the frame as described above.

The fibers are then cut along the length of the two end pieces creatingtwo individual webs of 100 fibers each that were approximately 610 mmlong. Both webs were laid out on a flat surface with the sides withoutthe 2^(nd) strip of film facing downward. A third piece of film was thenbonded in a similar fashion on top of the woven film on both ends of theweb, creating two 120 fiber webs with each end secured by a top film, abottom film, and a woven film.

To prepare the dead-end filter, a section of a web containing 16 fiberswas cut from a larger web. While holding the web on both ends, one endwas rotated 180°. The web was then folded in half, laying the taped endson top of one another. By this action the exit lumen of one fiber at thestart of the web is placed adjacent to the entrance lumen of thefurthest most fiber on the other side of the web. The web is rolled upat the taped ends to create a tight cylinder.

To compress the bundle into a solid mass, a 50 mm length of 12 mm ID FEP(1.3 to 1 ratio) heat shrinkable sleeve was subsequently placed over thebundled end placed into a tunnel heater at 218° C. for fifteen minutes.The bundle was removed and allowed to cool at room temperature forapproximately 20 minutes. The heat shrink sleeve was carefully scoredand removed from the bundled end.

Another small web of thirty-one fibers was twisted and folded in thesame fashion as the first web and rolled around the original bundle. A50 mm length of 38 mm ID FEP (1.6 to 1 ratio) heat shrink sleeving wasplaced over the bundle and heated at 218° C. for fifteen minutes. Thebundle was removed and allowed to cool at room temperature forapproximately twenty minutes, followed by removal of the FEP heat shrinksleeve. The process of preparing and folding web sections was repeatedusing webs of 63 fibers, 70 fibers, 80 fibers, 123 fibers, 50 fibers,each followed by compression with the appropriately sized FEP heatshrink and heating in the oven.

The final bundling process involves wrapping a 2,750 mm×5 mm wide stripof 0.127 mm THV 500G film/tape around the bundle and then placing a 5 mmlong piece of 76 mm diameter FEP heat shrink sleeving over the tape andheat at 232° C. for thirty minutes. The bundle is removed from the ovenand allowed to cool for forty-five minutes.

Following removal of the heat shrink sleeve, the final step in themethod can comprise trimming off 25 mm of the potted end for a freshclean finished bundle, exposing the open lumen ends. This finished“dead-end” cartridge produces an outside diameter of 67 mm, containing433 individual fibers with 886 open lumen ends with an active filtrationlength of 250 mm. Pull strength of individual fibers were measured asdescribed and averaged 70 N.

EXAMPLE 3

In this example, the film potting method is used to produce a doubleended cross flow module using double weaves. 200 loops of a hollow fibermembrane prepared from polytetrafluoroethylene with an inner diameter of1.5 mm and an outer diameter of 1.9 mm with a porosity of 65% werewrapped around a winding frame 1000 mm from end to end and 400 mm wide,fitted with slotted rods at each end, with spacing between slots of 2.0mm, ensuring spacing between the hollow fibers of 0.1 mm.

A potting tape prepared from Dyneon THV-220 with a thickness of 0.0762mm, a width of 25.4 mm, and a length of 600 millimeters (referred to asthe weave tape) was woven between each individual fiber at the end ofthe winding frame starting by passing under the first fiber, over theadjacent fiber, and continuing across the frame, resulting in a strip ofpotting film being interlaced between the fibers. The excess tape wastrimmed off.

After completing the initial weaving step, a second piece of the THV 220film of similar dimensions was woven next to the first piece of THVtape, reversing the weaving pattern from the first film. The secondpiece of film was woven by first passing the film over the first fiber,under the second fiber, and on until the second strip has been wovenbetween all the fibers. This weaving process was repeated at theopposite end of the frame.

A strip of film that is double the width of the individual weavingstrips but of the same length was placed on top of the hollow fibers(referred to as the top tape), directly above the woven strip. The endof the winding rack containing the tape was heated so that the film wasbrought above its melting point of 160° C. by means of a forced air heatgun set at 450° C. for 60 seconds. The potting tapes melted sufficientlyto attach to each other and to the hollow fibers. This process wasrepeated at the other end of the winding rack. The process was againrepeated on the two ends on the back side of the winding rack.

The fibers were cut at the ends of the winding frame to create twoindividual webs of fiber. Each web was placed on a flat surface with thetop strip facing downwards and another strip of film applied across thewoven strips and bonded in a similar fashion to the first side.

On completion of applying the potting film, the web is rolled up onitself. After rolling the 200 fiber web a diameter of approximately 46mm was achieved. A 50 mm long piece of 38 mm (1.3/1) FEP heat shrink andslide over each end of the bundle. Each potted end is placed in an ovenat 233° C. for a period of 30 minutes to achieve a finished diameter ofapproximately 39 mm after removing the FEP heat shrink.

The bundle was removed from the oven and allowed to cool for 30 minutes.Once cooled, the FEP heat shrink was removed and the second 200 fiberweb was rolled onto the compressed bundle resulting in a diameter ofapproximately 56 mm. Another 50 mm long piece of 60 mm FEP heat shrinkwas placed over each end of the bundle and placed in an oven at 232° C.for a period of 30 minutes to achieve a finished diameter of 51 mm. Thebundle was removed from the oven and allowed to cool for 30 minutes. TheFEP heat shrink was removed and approximately 25 mm was trimmed off ofeach bundled end resulting in a clean flush cut with open lumen ends.The average pull-out strength was measured at 68 Newtons.

EXAMPLE 4

In this example the tape potting method utilizing a spring steelcompression is used to produce a dead-end filter module.

200 loops of a hollow fiber membrane prepared frompolytetrafluoroethylene with an inner diameter of 1.0 mm and an outerdiameter of 1.4 mm with a porosity of 43% were wrapped around a windingframe equipped with slotted ends spaced at 1.5 millimeters, ensuringspacing between the hollow fibers of 0.1 mm.

A potting film prepared from Dyneon THV-220 with a thickness of 0.0762mm, a width of 25 mm, and a length of 400 mm was woven between eachindividual fiber at the end of the winding frame resulting in a patternwherein the tape was alternately passed over the top of one fiber andunderneath the adjacent fiber. A strip of film of similar size wasplaced underneath the hollow fibers, directly beneath the woven strip. Athird strip of film was placed above the woven strip. The end of thewinding rack containing the film was heated via a hot air gun set at450° C. for 45 seconds. The potting films melted sufficiently to attachto each other and to the hollow fibers.

The fibers were removed from the winding rack by cutting the fibersalong the major axis of the slotted end containing the film. One end ofthe hollow fiber membrane web was then folded over on itself resultingin a 180 degree twist in the web. The two taped ends were laid on top ofone another. The entire taped web was subsequently wound into a tightcylinder with the taped fiber ends wrapping up on themselves.

To achieve compression, the taped end was fitted with a sleeve of springsteel (0.178 mm 1095 grade tempered spring steel) approximately 130 mmlong by 5 mm wide. The sleeve of spring steel was in turn fastened withtwo hose clamps to allow compression of the spring steel. Each taped endwas then placed in an oven at 232° C. degrees for 30 minutes. Following15 minutes of heating, the bundle was removed and the hose clampstightened, resulting in a 10% reduction in the spring steel sleevediameter, compressing the bundle of fibers and molten tape into acontiguous mass. The process was continued 2 times. The resulting masswas allowed to cool for 30 minutes.

The potted bundle final diameter was 35 mm with a packing density of 78%in a dead end configuration. The resulting module was pressure tested byobserving the bubble point of the hollow fibers as outlined above and itwas found to have a fluid tight seal.

Subsequent testing of the individual fibers showed an average pullstrength of 71 Newtons.

EXAMPLE 5

The following example illustrates the use of a primer solution of thepotting resin to promote adhesion between the potting film and theporous PTFE hollow fibers being assembled into a module.

110 loops of a hollow fiber membrane prepared frompolytetrafluoroethylene with an inner diameter of 1.5 mm and an outerdiameter of 1.9 mm with a porosity of 65% were wrapped around a windingframe 400 mm from end to end and 250 mm wide, fitted with slotted rodsat each end, with spacing between slots of 2.0 mm, ensuring spacingbetween the hollow fibers of 0.1 mm.

After the fibers are secured to the winding rack, the ends of theindividual fibers are pretreated with a solution of the potting resin,in this example a solution of Dyneon THV 220 prepared by dissolving 3grams of THV 220 per 40 ml of acetone.

Using a synthetic bristle brush, a thin layer of the THV 220 solution isapplied to both ends of each fiber, ensuring that the full circumferenceof each fiber was coated. The coating was applied from the end of eachfiber in a distance equivalent to that of the potting film, in this case25 mm. Following application of the primer coating, the THV solution wasallowed to dry at room temperature for 120 minutes. After drying asecond layer of the THV solution was applied to the fibers. The secondcoating was allowed to dry at room temperature for an additional 120minutes.

A potting tape pre pared from Dyneon THV-220 with a thickness of 0.0762mm, a width of 25.4 mm, and a length of 600 millimeters (referred to asthe weave tape) was woven between each individual fiber at the end ofthe winding frame starting by passing under the first fiber, over theadjacent fiber, and continuing across the frame, resulting in a strip ofpotting film being interlaced between the fibers. The excess tape wastrimmed off.

After completing the initial weaving step, a second piece of the THV 220film of similar dimensions was woven next to the first piece of THVtape, reversing the weaving pattern from the first film, that is,passing over the first fiber, under the second fiber, and on until thesecond strip has been woven between all the fibers. This weaving processwas repeated at the opposite end of the frame.

A strip of film that is double the width of the individual weavingstrips but of the same length was placed on top of the hollow fibers(referred to as the top tape), directly above the woven strip. The endof the winding rack containing the tape was heated above its meltingpoint of 160° C. by means of a forced air heat gun set at 450° C. for 60seconds. The potting tapes melted sufficiently to attach to each otherand to the hollow fibers. This process was repeated at the other end ofthe winding rack. The process was again repeated on the two ends on theback side of the winding rack.

The fibers were cut at the ends of the winding frame to create twoindividual webs of fiber. Each web was placed on a flat surface with thetop strip facing downwards and another strip of film applied across thewoven strips and bonded in a similar fashion to the first side.

On completion of applying the potting film, the web is rolled up onitself. After rolling the 110 fiber web a diameter of approximately 35mm is achieved.

A 127 mm piece of 0.178 mm thick 1095 tempered spring steel was wrappedaround each end of the bundle and secured with two standard hose clamps.The potted ends were placed in an oven at 233° C. for a period of 30minutes. The bundle was removed and the hose clamps were tightenedapproximately 9 times to achieve an outside diameter of approximately26.5 mm or 25% of the original starting diameter. The potted ends wereallowed to cool for approximately 30 minutes and the clamps and temperedspring steel strip was removed. Approximately 25 mm was trimmed off eachpotted end resulting in a clean flush cut with open lumen ends. Anaverage pull strength of 81 Newtons was measured.

It should be noted that throughout this patent application, for the sakeof brevity, we use the term X/Y to represent a copolymer of X and Y, andthe term X/Y/Z to represent a terpolymer of X and Y and Z.

What is claimed is:
 1. A fluid transport device comprised of thefollowing: a cylindrical containment shell comprised of stainless steelin which contained within is: a plurality of non-meltingpolytetrafluoroethylene fibers having an inner diameter, an outerdiameter, two ends with a length between said ends, at least one end ofeach fiber open for fluid entrance or exit, said fibers arrangedparallel one another and bonded over a length region by a segment ofpolymeric film, said segment of polymeric film contacting outer surfaceareas of the fibers in the region and filling interstitial volumebetween the fibers in said region and; compression means on the exteriorsurface of the potted film that compresses the potted film during deviceassembly.
 2. The device of claim 1 wherein the fibers have a surfaceenergy of less than about 20 dyne-cm.
 3. The device in claim 1 whereinthe bundle of non-melting polytetrafluoroethylene hollow fibers that arebound together by at least one segment of film are heated above themelting point of the film at 80° C. to 300° C., and compressed, so thatthe melted film acts as the potting agent that binds the fibersresulting in densely packed fibers embedded in a solid mass, providing afluid-tight seal around each fiber with the open ends of the fiberexposed on one or both sides of the potted end or ends.
 4. The device inclaim 1 wherein the non-melting polytetrafluoroethylene hollow fibersare bound together in a densely packed fiber bundle by a fluoropolymerpotting agent film that binds the fibers on at least one end of thebundle in a solid mass, providing a fluid-tight seal around each fiber,and resulting in a potted bundle containing open ended fibers on thepotted end or ends.
 5. The device of claim 4 wherein said potting filmis selected from the group of materials comprising of perfluorinatedcopolymers of tetrafluoroethylene and hexafluoropropylene, copolymers oftetrafluoroethylene and alkoxy, copolymers of tetrafluoroethylene andperfluoropropylvinyl ether, copolymers of tetrafluoroethylene andchlorotrifluoroethylene, copolymers of ethylene and tetrafluoroethylene,ethylene and fluorinated ethylene propylene, tetrafluoroethylene-coperfluoro alkylvinyl ether and tetrafluoroethyleneco-hexafluropropylene.
 6. The device of claim 4 wherein said pottingagent film is comprised of fluorinated terpolymers comprising ofethylene and vinylidene fluoride and hexafluoropropylene.
 7. The deviceof claim 4 wherein the film around the fibers and the fiber bundle arecompressed by a cylindrical metal band with overlapping edges bound by aconstricting ring or rings that upon tightening results in the metalband to shrink in diameter.
 8. The device of claim 4 wherein the filmaround the fibers and the fiber bundle are compressed by a thermallyactivated shrinkable polymeric sleeve.
 9. The device of claim 4 whereinthe film around the fibers and the fiber bundle are compressed by acylindrical metal band with overlapping edges held by a collet that istightened as the bundle is heated causing the metal band to reduce indiameter.
 10. The device of claim 4 wherein the film around the fibersand the fiber bundle are compressed by a cylindrical metal band that isexpanded prior to application to the bundle after the placement of thefilm and then allowed to constrict in diameter with the use of aconstricting band.
 11. The device of claim 4 which after melting andcompressing the film around the fibers results in a packing density ofgreater than 65%.
 12. A hollow fiber membrane fluid transport devicecomprising a cylindrical containment shell comprised of stainless steel,and contained within the shell is a bundle of non-meltingpolytetrafluoroethylene hollow fibers, wherein the bundle is formed bytreating the fibers with a solvent polymer solution comprising a polymerused to prepare a potting film so that after the solvent is removed bydrying, the fibers are bound together by at least one segment of filminterwoven through interstitial spaces between the fibers and contactingthe fibers near or at the ends, and compression means on the exteriorsurface of the potted film that compresses the potted film during deviceassembly.
 13. The hollow fiber membrane fluid transport device in claim12 wherein the bundle of polytetrafluoroethylene hollow fibers treatedwith a solvent polymer solution are heated above the melting point ofthe film at 80° C. to 300° C., and compressed, so that the melted filmacts as a potting agent that binds the fibers resulting in denselypacked fibers embedded in a solid mass, providing a fluid-tight sealaround each fiber with the open ends of each fiber exposed on one orboth sides of the solid mass.
 14. The hollow fiber membrane fluidtransport device of claim 13 wherein the film comprises fluorinatedterpolymers of ethylene and vinylidene fluoride and hexafluoropropylene.15. The hollow fiber membrane fluid transport device of claim 12 whereinthe polytetrafluoroethylene hollow fibers treated with a solvent polymersolution are bound together in a densely packed fiber bundle by the filmused to bind the fibers on at least one end of the bundle in a solidmass, providing a fluid-tight seal around each fiber, and resulting in apotted bundle containing open ended fibers.
 16. The hollow fibermembrane fluid transport device of claim 12 wherein said film isselected from the group of materials consisting of perfluorinatedcopolymers of tetrafluoroethylene and hexafluoropropylene, copolymers oftetrafluoroethylene and alkoxy, copolymers of tetrafluoroethylene andperfluoropropylvinyl ether, copolymers of tetrafluoroethylene andchlorotrifluoroethylene, copolymers of ethylene and tetrafluoroethylene,and ethylene and fluorinated ethylene propylene.
 17. The hollow fibermembrane fluid transport device of claim 12 wherein the solvent polymersolution comprises a terpolymer of tetrafluoroethylene and vinylidenefluoride and hexafluoropropylene and solvents selected from the group ofmaterials consisting of acetone, methyl ethyl ketone, ethyl acetate,butyl acetate, and N-methyl pyrrolidone.
 18. The hollow fiber membranefluid transport device of claim 12 wherein the solvent polymer solutionis comprised of polymers selected from the group of polymers consistingof perfluorinated copolymers of tetrafluoroethylene andhexafluoropropylene, tetrafluoroethylene and alkoxy, tetrafluoroethyleneand perfluoropropylvinyl ether, tetrafluoroethylene andchlorotrifluoroethylene, ethylene and tetrafluoroethylene, ethylene andfluorinated ethylene propylene, and solvents selected from the group ofmaterials consisting of acetone, methyl ethyl ketone, ethyl acetate,butyl acetate, and N-methyl pyrrolidone.
 19. The hollow fiber membranefluid transport device of claim 12 wherein the film around the fibersand the fiber bundle are compressed by a cylindrical metal band withoverlapping edges bound by a constricting ring or rings.
 20. The hollowfiber membrane fluid transport device of claim 12 wherein the filmaround the fibers and the fiber bundle are compressed by a thermallyactivated shrinkable polymeric sleeve.
 21. The hollow fiber membranefluid transport device of claim 12 wherein the film around the fibersand the fiber bundle are compressed by a cylindrical metal band withoverlapping edges held by a collet that is tightened as the bundle isheated causing the metal band to reduce in diameter.
 22. The hollowfiber membrane fluid transport device of claim 12 wherein the filmaround the fibers and the fiber bundle are compressed by a cylindricalmetal band that is expanded prior to application to the bundle afterplacement of the film and then allowed to constrict in diameter with theuse of a constricting band.
 23. The hollow fiber membrane fluidtransport device of claim 12 which after melting and compressing thefilm around the fibers results in a packing density of greater than 65%.